The invention relates to a mobile crane including an undercarriage or lower crane carrying chassis, an upper load lifting and carrying chassis pivotally mounted on the lower chassis, a main boom pivoted on the upper chassis, and at least one further boom that can be connected to the main boom.
In the case of such a mobile crane, limits are set fundamentally with respect to its dimensions and thus with respect to possible load moments and lifting heights of loads. In general, such a mobile crane cannot be higher than four meters, no wider than three meters and its length is limited in general to seven to eight axles. With today's modern road construction including traffic circles and other constrictions, it is advantageous not to construct the mobile crane with maximum possible dimensions, so that it is maneuverable and can be advanced in densely populated regions without problems. Limits that may not be exceeded are also given with respect to its overall weight with a maximum axle load of twelve tons. On the other hand, the operating needs of such a mobile crane increasingly involve greater loads and constantly higher lifts. Therefore, mobile cranes have been provided with separate booms, where such separate boom is transported separately, for example, on a semitrailer truck or a specially designed transport vehicle. Thus, such separate booms can be built with greater dimensions than booms mounted directly on the mobile crane.
A known mobile crane disclosed in DE-A1 31 39 596 includes a crane travel frame, a crane upper carrying chassis attached to a rotary connection, and a separate telescopic boom. During the mounting of the latter on the crane upper carrying chassis, the crane travel frame and a boom transporter must first be coupled together backwards. This arrangement results in spatially limited mountability of the boom, because the space requirements do not always allow two extremely long travel frames or vehicles to be placed in succession. By telescoping the separate boom, such boom is slid by way of a sliding runway, which can be swung upwardly, onto the crane upper carrying chassis. After automatic bolting, on the one hand, and releasing of a hoisting cylinder, on the one hand, the boom can be lifted up when the crane is supported. Then, a counterweight can be deposited by the crane itself by way of a motor of the travel frame. By swivelling the crane upper carrying chassis, the mobile crane thus is moved into the actual operating state. With this crane high carrying forces and very long boom lengths can be obtained. However, such crane has the drawback that its assembly, erection and mounting, as explained above, is very complicated and time intensive and, therefore, not economical. In addition, the boom has to be loaded on a specially designed transporter, and an auxiliary crane must be provided to position massive and heavy plates that support the crane. Thus, the result is high acquisition costs and as a consequence high operating costs of this known system. Another drawback with this known mobile crane is that it can function only with a hydraulic boom. This significantly limits the field of application of the mobile crane.